Soldering of metals is well-known in art. It is a general practice to employ a fluxing agent during soldering to clean oxides and impurities from the surface of the metals and enable the formation of an effective solder joint.
Prior art solder fluxes generally yield flux residues which are corrosive and/or conductive. It has been a practice in the industry to wash these residues off the components after the soldering operation, especially for electronic components. The cleaning step normally involves the use of one or more halogenated organic solvents such as chlorofluorocarbons. However, there is a desire to eliminate the use of such solvents for ecological reasons.
Recently water cleanable solder fluxes and solder pastes have been introduced to the electronics industry. For example, Zado, U.S. Pat. No. 4,701,224, issued Oct. 20, 1987, discloses a solder flux which employs an ammonium halide salt as an activator. Although, the water-cleanable approach eliminates the use of organic solvents, it creates a waste water problem and the water cleaning step generally adds costs to the overall soldering process.
U.S. Pat. No. 4,940,498 issued Jul. 10, 1990 discloses a solder flux which employs a small amount of organic acid (e.g. 1-3% by weight) as an activator. The patent discloses that after the soldering operation, only negligible flux residues remain. However, it is known in the art that organic acids generally form tin and lead salts with soldering.
It is therefore an object of this invention to provide a solder flux and paste which does not require cleanup after the soldering operation.
Other objects and advantages will become apparent from the following disclosure.